1. Field of the Invention
The present invention relates to multi-section pendant supported telescopic booms and more particularly relates to a pendant pay-out or control system for preventing the boom from pivoting upwardly due to extension of the boom and downwardly due to retraction of the boom.
2. Description of the Prior Art
Multi-section, pendant supported telescopic booms for cranes or the like are well known in the art. It is also well known that such booms may be supported by pendant ropes that are located entirely externally of the boom, or may be of the type that have external pendant portions as well as internal pendant portions that are reaved around sheaves within the boom. Booms of the type having only external pendant ropes that are attached to, or near, the tip end of the boom and are trained over the upper end of a mast pivoted to the boom, or pivoted to the upper crane works, tend to raise the boom tip and decrease the angle between the mast and the boom in response to extension of the boom; and tend to lower the boom tip and to increase said angle in response to retraction of the multi-section boom.
The types of booms which are supported by pendants having both internal and external pendant portions such as disposed in the aforementioned Cozad application, operate in a reverse manner, i.e., the tip of the boom drops when extended and raises when retracted.
It is also well known in the art to extend and retract several sections of a multi-section boom with one or two hydraulic rams. U.S. Pat. No. 4,156,331, which issued to Lester et al on May 29, 1979 illustrates such a boom which uses two rams; and U.S. Pat. 4,133,411 which issued to Curb on Jan. 9, 1979 illustrates a boom operated by a single ram.